Q&A: Field-Applied Preservatives in a Flood Zone

Q: We are working in an AE flood zone where FEMA (Federal Emergency Management Agency) requires treated material to be used below the BFE (base flood elevation). But on this project, non-treated LVLs were installed instead. Are you aware of any preservative treatment that could be field-applied to LVLs (or any other type of non-treated framing) to meet FEMA requirements?

If treated wood that meets AWPA standards is required (by FEMA, local building codes, architectural specifications, or the like) but untreated wood was installed, there is generally nothing you can do to the wood in the field to make it conform to those standards.

Most of the materials listed in our standards are pressure treated in a commercial facility or—in the case of composite products such as treated OSB—the components are mixed with preservatives before the product is manufactured.

Nevertheless, there are cases when nonconforming material has been installed and the governing authority or engineer of record will decide to mitigate potential problems through topical field treatment rather than force a builder or homeowner to demolish the structure and start over.

When a variance allowing field treatment is permitted, we normally suggest the use of topical preservatives with the explicit understanding that the field-treated wood does not have the same degree of protection as pressure-treated wood conforming to AWPA standards, and one should not expect the same performance or level of durability as with properly treated wood.

In recent inquiries from FEMA representatives regarding this topic, they indicated they knew that untreated products could not be made to conform to AWPA standards. That said, they were looking at types of field-applied products that would provide the best performance so that the homeowner could avoid having to rebuild the structure.

For this application where the wood is not expected to be exposed to precipitation, they were most interested in the use of a water-?soluble boron-based wood preservative. (Regular exposure to precipitation can significantly reduce the long-term effectiveness of boron-based preservatives). Then, because floodwaters could easily absorb the boron and remove it from the wood over time, they considered applying several additional coats of a topical oil-based water-repellent finish to reduce the amount of water that could be absorbed by the boron-treated wood during a flood. Again, this treatment would not be as effective as wood treated to AWPA standards, but at least the structure would not need to be torn down if a variance allowed for this type of remedial treatment.